Object visible in preview disappears when I render
Look at the camera icons on the outliner. When the camera icons are disabled, the object is disabled from rendering.
Click on the funnel icon on the top right and enable different filters.
The Eye icon determines visibility in the 3d viewport.
The Monitor icon disables the object in all viewports.
The Camera icon determines if the object is rendered or not.

https://docs.blender.org/manual/en/latest/editors/outliner/interface.html
For version 1.79 or older the controls are like this: